# The Case of the Missing Rectangle Side

• Fourth Grade
• Math
• 65 minutes
• Standards: 4.MD.A.3
• no ratings yet
August 15, 2015

Your students will become junior math detectives as they hunt down the missing side of a rectangle by applying the area formula for rectangles. The only clues they have are the rectangle’s area and the measure of one side.

### Learning Objectives

Students will be able to find the missing side of a rectangle given the rectangle’s area and measure of one side by applying the area formula.

## Lesson

### Introduction (10 minutes)

• Prior to the lesson, draw a large rectangle to display.
• Tell students that today they will be on the case of the missing rectangle side.
• Inform them they will need their multiplication, division, and reasoning skills to solve the case.
• Display the large rectangle. Add to the fun by drawing a magnifying glass, and tell students that they are officially on the case of the “missing rectangle side."
• Tell students that the only clues they have on the case is the area of the rectangle and the measure of one of the rectangle’s sides.
• Write down the label area underneath the rectangle, defining it as the space inside the shape.
• Next, review the formula for area.
• Write down the area formula. Demonstrate an example of solving for area.

### Explicit Instruction/Teacher Modeling (10 minutes)

• Begin by writing down several area problems.
• Ask students to solve the problems.
• On your chart paper, draw a rectangle. List one side and display the area.
• Next to the unknown rectangle side, write an X.
• With student input, develop a formula for the missing side.
• Display your formula on your chart paper. For example, 12 x (X) = 36.
• Ask students how they think this formula can be solved.
• Discuss strategies, and solve.

### Guided Practice/Interactive Modeling (10 minutes)

• Draw another rectangle with an unknown side.
• Display one side and the area of the rectangle.
• Ask students to solve the problem on their own.
• Check their answers.

### Independent Working Time (15 minutes)

• Ask students to draw 4 rectangles on a piece of notebook paper.
• Direct your students to write down the area and the measure of one side next to the rectangle and an X for the missing side.
• Have students exchange papers with partners.
• Instruct your students to solve for all missing sides on their papers.
• After they have completed their work, have them return to their partners to correct the work.
• Have your students discuss any errors with each other.
• Walk around, and monitor student discussion. Intervene with struggling students as necessary.
• Collect student work to assess.

## Extend

### Differentiation

• Enrichment: Ask a small group to develop a real life story problem in which there is an unknown variable for a rectangle where the area and one side is given. In the whole group, present the story problem the small group has written, and have all students solve.
• Support: Students may struggle solving for the unknown side if they do not have strong basic multiplication and division skills. Work with them in a small group to review these skills.

## Review

### Assessment (10 minutes)

• Look over student work.
• Provide feedback on student papers.

### Review and Closing (10 minutes)

• Take the story problems that your advanced students wrote during enrichment.
• Have students come up and read their story problem to the class.
• Solve the problems as a whole group.

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